In Mobile Satellite System (MSS) networks, antenna performance at the mobile terminal is critical in determining the performance of the overall system. Considerable development work has thus been performed globally relating to performance and implementation of antenna designs that are suitable for terminals in such networks.
Patch antennas were initially considered because of their low physical profiles, and their theoretical peak gains of greater than 7 dB. In practical implementations, however, much lower peak gains were achieved. Furthermore, these antennas have narrow frequency bandwidth performance, and poor axial ratio performance at off-boresite angles, thus typically limiting their coverage to 25 degree elevation angles.
The aforementioned low antenna gain has been addressed by using phased array techniques which involve driving multiple antenna elements in parallel using a phased drive network. This enables higher overall antenna gain to be achieved while accepting lower gains from the individual antenna elements. High gain phased-array antenna arrangements using patches, with either manual or automatic antenna pointing, can typically provide between 9 dB and 18 dB of antenna gain. The phased array drive networks introduce undesirable losses into the antenna arrangements, however, and are complex to design across a broad range of operating frequency.
Low gain passive antennas using multifilar helices or patch elements have been used in MSS networks, typically exhibiting antenna gains up to 6 dB.